Method of metallurgically bonding articles and article therefor

ABSTRACT

An article suitable for laser-welded metallurgical bonding, the article having a first part having a lower surface, and a second part having an upper surface is disclosed. The lower surface of the first part is disposed at the upper surface of the second part to provide for a faying surface thereat. The faying surface has a plurality of channels with a depth equal to or greater than about 1 micron and equal to or less than about 1000 microns. The article is suitable for laser-welded metallurgical bonding at the faying surface. The plurality of channels has a repetitive pattern of channels arranged along a path of the faying surface in a direction of the metallurgical bonding action.

BACKGROUND OF THE INVENTION

The present disclosure relates generally to a method of metallurgicallybonding an article and an article suitable therefor, and particularly toa surface condition at the article for improving the metallurgical bond.

Vehicle fabrication and assembly may involve a number of metallurgicalbonds, such as welds for example, that may be time consuming to createand may require special considerations depending on the materials beingbonded. The welding of galvanized parts, or galvanized to aluminumparts, may offer a challenge to the weld practitioner since zinc vaporfrom the coated steel, and magnesium vapor from magnesium-bearingaluminum alloys, is released at the weld site due to the high vaporpressures or low melting points of the respective materials. As aresult, the entrapped vapors may introduce contaminants and/or voidswithin the solidified weld nugget.

Also of consideration to the weld practitioner may be the thickness ofthe parts being metallurgically bonded. For example, ultra-thin gagesteel, having a thickness on the order of about 0.7 millimeters forexample, may be difficult to resistance weld due to the large heat lossat the faying surface to the copper electrodes. The heat build-up at theelectrodes tends to cause electrode material softening and facilitatesthe inter-diffusion between the electrode material and the zinc-richcoating on a galvanized steel surface, which in turn may accelerateelectrode wear. As the electrode wears and the cap face flattens, thecurrent density at the electrode-to-sheet interface decreases, resultingin a decrease in weld nugget size in the absence of compensatingadjustments. One compensating adjustment may be to dress the electrodeface as the electrode starts to wear, which may be time consuming andmay be disruptive to high volume production processes.

Another consideration to the weld practitioner may be the use ofhydroformed parts, which tend to have thin shells and may experienceweld distortion and cracking at the weld site due to the high electrodeforce and the high weld temperatures required to produce a satisfactoryweld.

Accordingly, there is a need in the art of metallurgical bonding methodsand arrangements that overcome these drawbacks.

SUMMARY OF THE INVENTION

Embodiments of the invention disclose an article suitable forlaser-welded metallurgical bonding having a first part having a lowersurface, and a second part having an upper surface. The lower surface ofthe first part is disposed at the upper surface of the second part toprovide for a faying surface thereat. The faying surface has a pluralityof channels with a depth equal to or greater than about 1 micron andequal to or less than about 1000 microns. The article is suitable forlaser-welded metallurgical bonding at the faying surface. The pluralityof channels has a repetitive pattern of channels arranged along a pathof the faying surface in a direction of the metallurgical bondingaction.

Further embodiments of the invention disclose a method ofmetallurgically bonding an article by laser welding. A first part havinga lower surface is placed against a second part having an upper surfaceto provide for a faying surface at an interface of the lower and theupper surfaces. The faying surface has a plurality of channels having adepth equal to or greater than about 1 micron and equal to or less thanabout 1000 microns. The first and the second parts are pressed againstone another, and heat is applied from a laser welding device to thefirst part such that the heat crossing the interface of the lower andthe upper surfaces results in melting at the interface and capillaryfluid flow of the metallurgical molten material within the plurality ofchannels. The laser welding device is moved along a path to define ametallurgical bonding action. The plurality of channels has a repetitivepattern of channels arranged along a path of the faying surface in adirection of the metallurgical bonding action. The faying surface iscooled thereby producing a laser weld metallurgical bond at the fayingsurface of the article.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring to the exemplary drawings wherein like elements are numberedalike in the accompanying Figures:

FIG. 1 depicts an exemplary article suitable for welding in accordancewith embodiments of the invention;

FIG. 2 depicts a partial end view of the article of FIG. 1;

FIG. 3 depicts an alternative partial end view of the article of Figurel;

FIGS. 4-8 depict plan views of alternative patterns of channels for usein embodiments of the invention;

FIGS. 9-14 depict partial section views through the article of FIG. 1with additional process features illustrated;

FIG. 15 depicts a plan view of a foot of a weld bead as it moves in adirection of welding and as used in embodiments of the invention;

FIG. 16 depicts a side view of the weld bead of FIG. 15;

FIG. 17 depicts an end view of a weld made along an edge of an articlein accordance with embodiments of the invention; and

FIG. 18 depicts a flow chart of a method for use in accordance withembodiments of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the invention provide an article having a first part anda second part that is suitable for metallurgical bonding, and a methodfor metallurgically bonding the article. In particular, the first partmay be a door panel of an automobile and the second part may be asupport structure of the automobile to which the door panel is bonded.The first part may be made from coated metal, such as galvanized steelfor example, and the second part may be made from steel, aluminum, orany other material suitable for metallurgical bonding. The second partmay also be made using a hydroforming process. The metallurgical bondmay be accomplished using resistance welding, arc welding, laserwelding, or any other process suitable for producing a metallurgicalbond at a faying surface, such as electron beam welding or hybrid laserwelding for example. As used herein, the term faying surface refers tothe bonded region where a first surface of the first part interfaceswith a second surface of the second part. Grooves, or channels, formedin the article at the faying surface prior to welding provide a meansfor venting vaporized particles and or gases at the weld site duringwelding to diminish the occurrence of voids in the resultant weld, andfor providing capillary action at the weld site to broaden the footprintof the resultant solidified weld and constrict heat flow through theinitial contact points between the first and second parts. The capillaryaction within the channels is a result of the capillary pressure betweenmolten fluid and the wetted metal, which builds up to pull the moltenmetal outward from the weld center whereby both the first and secondparts form a metallurgical bond. The channels, or micro-channels as theyare also herein referred to, also serve as routes for the molten metalto flow outward away from the welding center, the outward flow being aresult of the higher pressures at the welding center versus thesurrounding regions.

FIG. 1 depicts an exemplary article 100 having a first part 110 with alower surface 112 and a second part 120 with an upper surface 122. Asdiscussed previously, first part 110 may be a door panel for example,and second part 120 may be a support structure for example. Duringmetallurgical bonding of first part 110 to second pan 120, lower surface112 is disposed at upper surface 122 thereby providing for a fayingsurface between the two. The faying surface includes a plurality ofchannels 130 that are formed in upper surface 122 by laser or electronbeam micro-machining, embossing, machining, rolling, scribing, or anyother suitable method for producing micro-channels, such as knurling forexample. In an embodiment, channels 130 have a nominal depth “d” equalto or greater than about 1 micron (or micro-meter, μm) and equal to orless than about 1000 microns, and a nominal width “c” equal to orgreater than about 10 microns and equal to or less than about 1000microns. In an alternative embodiment, “d” is equal to or less thanabout 200 microns, and “c” is equal to or less than about 100 microns.Due to their small dimensions, channels 130 are also referred to asmicro-channels. Embodiments described herein depict channels 130 onupper surface 122, however, channels 130 may be on lower surface 112 oron both upper and lower surfaces 122, 112. In an embodiment having aplurality of channels 130 on both upper and lower surfaces 122, 112, thetwo sets of channels may be arranged orthogonal to each other.

FIGS. 2 and 3 illustrate two different partial end views of article 100of FIG. 1, with each Figure depicting channels 130 in an exaggeratedscale and idealized cross-sectional geometry relative to the dimensionsof second part 120. In FIGS. 2 and 3, only the top section of therectangular hydroformed second part 120 is shown, the bottom and sidesections being removed for clarity. In FIG. 2, channels 130 are formedsuch that upper surface 122 is planar, while in FIG. 3, channels 130 areformed such that upper surface 122 has ridges 132, 134 on either side ofvalley 136, which may be formed in a manner discussed previously. Indifferent embodiments, ridges 132, 134 may be the same height relativeto the floor of valley 136, or they may be of different heights. Ridges,or lips, 132, 134 may be formed in a snowplow-like manner using amechanical instrument or a laser, where thermocapillary convectiondrives outward motion of the fluid from the evolving channel 130. Thedisplaced material then solidifies along the banks of channels 130. Ascan be seen by reviewing the channels 130 of FIGS. 2 and 3, ridges 132,134 (see FIG. 3) provide an extended surface area, or length incross-sectional view, at the banks of channel 130, as compared to achannel 130 absent ridges 132, 134 (see FIG. 2). In an embodiment,ridges 132, 134 have a height relative to surface 122 that is equal toor less than the depth “d” of the corresponding channel 130. In anembodiment where the height of ridges 132, 134 is less than depth “d” ofchannel 130, the ridges 132, 134 may act as mechanical grippers duringbonding, as well as acting to provide additional venting of gases andthe like. Exemplary channels 130 and/or ridges 132, 134 have adirectional topography associated with them, thereby enabling theventing discussed herein. The uniformity of channels 130 depicted inFIGS. 2 and 3 is for illustration purposes only, and channels 130 may bearranged in a variety of different ways, as depicted in FIGS. 4-8, whichwill now be discussed in further detail.

In FIG. 4, exemplary channels 130 include a first plurality of channels140 and a second plurality of channels 150. In an embodiment, firstplurality of channels 140 are straight lines that radiate from a center160, and second plurality of channels 150 are concentric circlesarranged about center 160. In an alternative embodiment, first pluralityof channels 140 may be curvilinear, and second plurality of channels 150may be arranged in other shapes, such as a polygon for example, wherefirst and second channels 140, 150 are interconnected. The channelpattern 130 of FIG. 4 may be suitable for resistance welding where theupper and lower electrodes are aligned on center 160. However, todesensitize the quality of the weld to alignment considerations,alternative channel patterns may be preferable.

In FIG. 5, an alternative arrangement of channels 130 includes a firstplurality of channels 140 having horizontal, vertical and diagonallines, and a second plurality of channels 150 arranged in a circle abouta center 160. While FIG. 5 depicts only one circular channel 150, itwill be appreciated that a repeat pattern of channels 130 will provide aplurality of circular channels 150 about different but similarlyarranged centers 160. A repeat arrangement of channels 130, as depictedin FIG. 5, may be arranged in a strip, as depicted in FIG. 6. Referringto FIG. 6, channels 130 may be formed in upper surface 122 of secondpart 120 by a rolling process, where a rolling tool (not shown) has thechannel pattern of FIG. 5 embossed on an outer surface of a roller in arepeating arrangement, and where the roller is rolled in the directionof arrow 170. Alternatively, a laser or electron beam device (not shown)may micro-machine the channels 130 into upper surface 122 while thelaser head moves in the direction of arrow 170.

FIG. 7 depicts another strip arrangement of channels 130 that includesat least one linear channel 180 having a direction that is the same asthe direction of a metallurgical bonding action, the direction beingrepresented by arrow 170 and discussed in more detail later, and aplurality of rib-like channels 190 forming parallel lines on either sideof the at least one channel 180, the channels 190 being slanted at anangle relative to the direction of the bonding action. In an embodiment,the plurality of rib-like channels 190 are slanted in a direction thatis the same as the direction of the metallurgical bonding action 170.

FIG. 8 depicts a similar arrangement to that of FIG. 7, but withmultiple central linear channels 180, and with rib-like channels 190that may vary in length as the pattern is repeated in the direction ofarrow 170. The oval 200 in FIG. 8 represents an arc or laser weld beadhaving a diameter “D” that travels in the direction of arrow 170 duringthe welding process, which will be discussed in more detail later.

In viewing the channel patterns depicted in FIGS. 5, 6 and 8, it will beappreciated that weld bead 200 may not necessarily need to be alignedwith a particular center 160, as discussed previously in relation toFIG. 4, since there are multiple channels 140, 180 running parallel tothe direction of arrow 170 (direction of arc or laser welding), andmultiple intersections (similar to centers 160) between a firstplurality of channels 140, 180 and a second plurality of channels 150,190.

First with respect to resistance welding, and referring now to FIGS. 9and 10 that depict a partial section view through an article 100 similarto that of FIG. 1 where the section plane is the plane of the paper andperpendicular to line “L”, a method for resistance welding article 100is depicted in illustration form. As discussed previously, article 100includes a first part 10 and a second part 120, where second part 120has a plurality of channels 130 disposed at an upper surface 122. Upperand lower electrodes 210, 220, respectively, are pressed against firstand second parts 110, 120, thereby forcing first and second parts 110,120 against one another. An electrical current, which may be alternatingcurrent (AC), direct current (DC) or pulsed current, passes betweenelectrodes 210, 220 and across the interface 230 of the upper and lowersurfaces 112, 122 to result in melting small amounts of surfaces 112 and122 at the interface, and capillary fluid flow of the metallurgicalmolten material within the plurality of channels 130. FIG. 9 representsthe beginning of the weld process, and FIG. 10 represents the end of theweld process. As depicted in FIG. 9, molten sites 240 are initiatedalong the ridge lines of channels 130 where lower surface 112 interfaceswith upper surface 122. As the welding process continues, vaporizedmaterial, and particularly vaporized zinc from galvanized steel orvaporized aluminum or magnesium from a hydroformed part, vents away fromthe weld site via the plurality of channels 130, thereby reducing theoccurrence of contaminants that may result in voids in the resultantsolidified weld. Additionally, channels 130, as a result of theirpredetermined dimensions, provide a capillary action to force the moltenmaterial away from the center of the weld site, thereby broadening thecross-section of the resultant weld. Zinc coating on first and/or secondparts 110, 120 has a lower boiling point temperature (about 906degree-Celsius) than the underlying substrate, which in an embodimentmay be steel for example, resulting in vaporized contaminants at theweld site that may be undesirable. The incorporation of appropriatelydimensioned channels 130 aids in the removal of these contaminants foran improved resultant weld. Cooling of the faying surface produces ametallurgical bond at the faying surface having fewer voids than wouldbe present in the absence of the plurality of channels 130, and wherethe overall dimension “X” of the resultant weld is greater than it wouldbe in (he absence of the plurality of channels 130, represented bydimension “Y”. The difference between dimensions “X” and “Y” isattributed to the capillary forces at play during the welding processdue to the presence of channels 130 and the pressure differences betweenpressed and non-pressed areas. In an embodiment, the overall dimension“R” of the plurality of channels 130 is greater than the overalldimension “X” of the resultant metallurgical bond, thereby maximizingthe venting and capillary effect of channels 130.

Also, resistance welding with micro-channels 130 may be advantageouswhere first and/or second parts 110, 120 may be thin, such as equal toor less than about 1 millimeter (mm), or equal to or less than about 0.7millimeter, since the resultant weld can be desensitized to electrodewear.

Reference is now made to FIGS. 11-14, which parallel the illustrationsof FIGS. 9 and 10, except for illustrating different welding processes.FIGS. 11 and 12 depict laser welding at the initial stage (FIG. 11) andat the end stage (FIG. 12), while FIGS. 13 and 14 depict arc welding atthe initial stage (FIG. 13) and at the end stage (FIG. 14). With bothlaser and arc welding, first and second parts 110, 120 are pressedagainst one another with a plurality of channels 130 being disposed onthe upper surface 122 of second part 120, similar to the arrangementdiscussed previously. Heat is applied to first part 110 via a laserwelding device 250 or an arc welding device 260 in such a manner thatheat crossing the interface of lower and upper surfaces 112, 122 resultsin melting at the interface, venting of vaporized contaminants, such aszinc and/or magnesium vapor, away from the weld site via channels 130,and capillary fluid flow of the metallurgical molten material within theplurality of channels 130. Arrows 270, 280 point to the areas,illustrated as a sideways bulges, at channels 130 where venting andcapillary action occurs. Laser and arc welding devices 250, 260 movealong a path defined by line “L” (see FIG. 1) in a direction of arrow170 (into the page when viewing FIGS. 11-14) to define a metallurgicalbonding action. In an embodiment that metallurgically bonds article 100via laser or arc welding, channels 130 may be made up of a repetitivepattern of channels similar to those depicted in FIGS. 5-8, anddiscussed previously. Laser and arc welding methods employed in themanner described herein may be suitable for bonding thin gage galvanizedsteel, having a thickness of equal to or less than about 1 millimeter,or equal to about 0.7 millimeter, to hydroformed support structures.

Referring now to FIGS. 15 and 16, where FIG. 15 depicts a plan view ofthe foot of weld bead 200 as it moves in the direction of arrow 170, thedirection of welding, and FIG. 16 depicts a side view of FIG. 15. FIG.16 is also representative of a side view of the welding action depictedin FIGS. 11 and 13. FIG. 17, having a view orientation similar to thoseof FIGS. 11 and 13 where movement of the welding device 250, 260 is intothe plane of the paper, illustrates that a laser and an arc weldingprocess may also be performed along an edge of first part 110. In FIG.17, the region of channel venting and capillary action is depicted byarrow 270, 280.

In order to determine the size and quantity of channels 130 foreffective vapor venting and capillary action, several calculations needto be performed (assuming a spatially constant pitch), which will now bedescribed in more detail with reference to FIGS. 15 and 18.

FIG. 18 depicts a method 300 for calculating the size and quantity ofchannels 130 that begins at block 310 where the pressure ΔP_(AB)required to prevent the coating vapor from entering a weld pool duringwelding is estimated. See FIG. 15 for reference to location AB ofΔP_(AB). The equation for the pressure is given by Equation-1.ΔP _(AB)=ρ_(L,Fe) gT _(p)  Equa.-1

-   -   where:    -   P_(L,Fe) is the density of liquid iron    -   g is gravity    -   T_(p) is the thickness of galvanized steel (first part).

At block 320, the escape velocity V_(B) of the coating vapor isestimated. Using the Bernoulli equation, the equation for the velocityis given by Equation-2.V _(B)=(2ΔP _(AB)/ρ_(v,Co))^(0.5)  Equa.-2

-   -   where:    -   ρ_(v,Co) is the density of the coating vapor.

At block 330, the mass flow rate m of the coating vapor is estimated.The equation for the mass flow rate is given by Equation-3.m=2T _(Co) V _(W)(W+2b)ρ_(s,Co)  Equa.-3

-   -   where:    -   T_(Co) is the thickness of the coating (Zinc for example)    -   V_(W) is the welding speed    -   ρ_(s,Co) is the density of solid coating (Zinc for example)    -   (W+2 b) is depicted in FIG. 15, where W is the width of the        weld, and b is the boiling width of the coating (Zinc for        example).

At block 340, the volume flow rate V of the coating vapor is calculated.The equation for the volume flow rate is given by Equation-4.V=m/ρ _(v,Co)  Equa.-4

At block 350, the channel area and quantity of channels for venting thecoating vapor away from the weld pool is calculated. However, thesevalues are derived in the following manner.

If there is a total channel area A that allows the coating vapor toescape, then the volume flow rate V of the coating vapor is provided byEquation-5.V=V _(B) A.  Equa.-5

Equating Equation-5 to Equation-4, substituting in Equation-3 for m, andsolving for area A with the conservation of the coating vapor beingconsidered, gives:A=(2T _(Co) V _(W)(W+2b)ρ_(s,Co))/(ρ_(v,Co) V _(B)).  Equa.-6

Substituting Equations-1 and 2 into Equation-6, gives:A=(2^(0.5) T _(Co) V _(W)(W+2b)ρ_(s,Co))/(ρ_(v,Co)ρ_(L,Fe) gT_(p))^(0.5)  Equa.-7

Further derivation assumes that the channel cross-section isrectangular, even though in practice the channel corners may be rounded.The channel cross-sectional dimensions are governed by the balancebetween molten fluid surface tension and the mean pressure from themolten fluid in the keyhole (a vapor cavity in the part being welded,caused by the welding device, that is filled in by the flow of moltenfluid) that leads to imperfect wetting of the channels by the moltenfluid. Imperfect wetting is desirable since it leads to slower heatextraction and minimal thermomechanical distortion and cracking withoutcompromising mechanical interlocking between the solidified material andthe channels. In view of these considerations, the channel width, c, isgiven by:c=(4d((2γ/P)−d)))^(0.5)  Equa.-8

-   -   where:    -   d is the channel depth    -   γ is the surface tension of the molten metal in the keyhole    -   P is the mean fluid pressure.

The channel width, c, is related to the channel pitch, λ, byc=fλ  Equa.-9

-   -   where the channel pitch is defined as the distance between the        centers of adjacent channels, and:    -   0<f<1.

Assuming a channel length of L_(c), then the total number of channels,Q_(c); required isQ _(c) =A/(L _(c) c).  Equa.-10

Exemplary values for variables presented in Equations 1-10 are asfollows:

-   -   ρ_(v,Co)=21.87 kg/m³ (kilogram/meter³), (where the coating is        Zinc)    -   ρ_(s,Co)=7135 kg/m³, (where the coating is Zinc)    -   ρ_(L,Fe)=7320 kg/m³    -   g=9.8 m/s² (meter/second²)    -   V_(W)=1 m/min (meter/minute)    -   T_(Co)=9.81 μm    -   T_(p)=3 mm    -   W=3 mm    -   b=−0 (boiling width of zinc)    -   γ=2 N/m (Newton/meter), (where the metal is iron).

In an exemplary embodiment, article 100 includes rib-like channels 190having a pitch λ equal to or greater than about 7 millimeters and equalto or less than about 22 millimeters, more preferably, pitch λ is equalto or greater than about 11 millimeters and equal to or less than about13 millimeters, and even more preferably, pitch λ is equal to about 12millimeters.

In an exemplary embodiment having a channel width c of about 100 micronsand a channel depth d of about 200 microns, about 7 channels arerequired for each piece of galvanized steel.

In another exemplary embodiment using resistance welding with a weldcurrent of about 10.2 kilo-amps, an electrode weld force of about 480pounds, and a weld time of about 14 cycles, it was observed that theweld diameter increased from about 5.1 millimeters to about 6.1millimeters with the introduction of micro-channels in accordance withembodiments described herein.

As disclosed, some embodiments of the invention may include some of thefollowing advantages: reduced number of voids at the weld site;increased foot print at the weld site that contributes a mechanicalinterlocking component to the overall bond; increased tensile strengthat the weld site; ability to weld ultra thin gage steel; reduced need toredress electrode face as a result of electrode wear during resistancewelding; the desensitization of spot welding on thin steel to variationsin electrode diameter; reduced manufacturing cost and weight as a resultof being able to weld with hydroformed parts; reduced distortion at theweld site of the welded part; and, low equipment cost as a result ofrequiring only a single laser with laser welding.

While the invention has been described with reference to exemplaryembodiments, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment disclosed as the best oronly mode contemplated for carrying out this invention, but that theinvention will include all embodiments falling within the scope of theappended claims. Moreover, the use of the terms first, second, etc. donot denote any order or importance, but rather the terms first, second,etc. are used to distinguish one element from another. Furthermore, theuse of the terms a, an, etc. do not denote a limitation of quantity, butrather denote the presence of at least one of the referenced items.

1. An article suitable for laser-welded metallurgical bonding, thearticle comprising: a first part having a lower surface; and a secondpart having an upper surface, the lower surface of the first partdisposed at the upper surface of the second part to provide for a fayingsurface thereat; wherein the faying surface comprises a plurality ofchannels having a depth equal to or greater than about 1 micron andequal to or less than about 1000 microns, the article being suitable forlaser-welded metallurgical bonding at the faying surface; wherein theplurality of channels comprises a repetitive pattern of channelsarranged along a path of the faying surface in a direction of themetallurgical bonding action.
 2. The article of claim 1, wherein therepetitive pattern of channels comprises a pattern of intersectinglinear lines and curvilinear lines arranged along a path of the fayingsurface in the direction of the metallurgical bonding action.
 3. Thearticle of claim 2, wherein the intersecting linear lines define atleast one center, and at least one curvilinear line is disposed aboutthe center.
 4. The article of claim 1, wherein the repetitive pattern ofchannels comprises at least one line having a direction that is the sameas a direction of the metallurgical bonding action, and a plurality ofrib-like lines forming parallel lines on either side of the at least oneline.
 5. The article of claim 4, wherein the plurality of rib-like linesare slanted in a direction that is the same as a direction of themetallurgical bonding action.
 6. The article of claim 4, wherein therib-like lines have a pitch equal to or greater than about 7 millimetersand equal to or less than about 22 millimeters.
 7. The article of claim6, wherein the rib-like lines have a pitch equal to or greater thanabout 11 millimeters and equal to or less than about 13 millimeters. 8.The article of claim 1, wherein at least one of the first part and thesecond part has a thickness equal to or less than about 1 millimeter. 9.The article of claim 1, wherein at least one of the first part and thesecond part comprises a hydroformed part.
 10. The article of claim 1,wherein at least one of the first part and the second part comprises asubstrate and a coating on the substrate disposed at least at the fayingsurface, the coating having a lower boiling point temperature than thesubstrate.
 11. The article of claim 10, wherein the coating is zinc. 12.The article of claim 10, wherein the plurality of channels has across-sectional area calculated using at least two of: the thickness ofthe coating; the welding speed; the density of solid coating material;the density of vaporous coating material; and the density of moltensubstrate material.
 13. A method of metallurgically bonding an articleby laser welding, the method comprising: placing a first part having alower surface against a second part having an upper surface to providefor a faying surface at an interface of the lower and the uppersurfaces, the faying surface comprising a plurality of channels having adepth equal to or greater than about 1 micron and equal to or less thanabout 1000 microns; pressing the first and the second parts against oneanother; applying heat from a laser welding device to the first partsuch that the heat crossing the interface of the lower and the uppersurfaces results in melting at the interface and capillary fluid flow ofthe metallurgical molten material within the plurality of channels;moving the laser welding device along a path to define a metallurgicalbonding action, the plurality of channels comprising a repetitivepattern of channels arranged along a path of the faying surface in adirection of the metallurgical bonding action; and cooling the fayingsurface thereby producing a laser weld metallurgical bond at the fayingsurface of the article.
 14. The method of claim 13, wherein: the firstpart comprises a substrate having a coating disposed at least at thelower surface of the substrate, the coating having a lower boiling pointtemperature than the substrate; in response to the heat at theinterface, the coating at least partially vaporizes, and the vaporizedmaterial at least partially escapes away from the faying surface via theplurality of channels; and the cooling of the faying surface results ina metallurgical bond having fewer voids than would be present in theabsence of the plurality of channels.
 15. The method of claim 14,wherein the coating is zinc.
 16. The method of claim 13, wherein atleast one of the first part and the second part has a thickness equal toor less than about 1 millimeter.
 17. The method of claim 16, wherein atleast one of the first part and the second part has a thickness equal toor less than about 0.7 millimeter.
 18. The method of claim 13, whereinthe resulting metallurgical bond has a width greater than would bepresent in the absence of the plurality of channels.
 19. The method ofclaim 18, wherein the faying surface comprises a coating, and furthercomprising: estimating the pressure required to prevent coating vaporfrom entering a weld pool during welding; estimating an escape velocityof the coating vapor; estimating a mass flow rate of the coating vapor;computing a volume flow rate of the coating vapor; and computing achannel area and a quantity of channels for venting the coating vaporaway from the weld pool.
 20. The method of claim 19, wherein the coatingis zinc.
 21. An article made by the method of claim 19.